Electromechanical oscillator with isochronous compensation and/or frequency regulation

ABSTRACT

An electromechanical oscillator having an oscillating member which is electrically maintained in mechanical oscillation, in which a pair of magnets with opposite poles defining a gap is carried by a single oscillating member or by one or both tines of a tuning fork, and the rotor is so mounted that the wavy magnetic tracks pass through the gap or gaps between the pair(s) of magnets. There may be a magnetic member adjacent the free pole of one magnet to provide isochronous compensation or frequency regulation, or a member to provide isochronous compensation adjacent the free pole of one magnet of a pair and a member to provide frequency regulation adjacent the free pole of the other magnet of the pair.

United States Patent Clifford [4 1 July 18, 1972 [54] ELECTROMECHANICAL OSCILLATOR 3,338,047 8/1967 Kueffer... ..58/23 WITH ISOCHRONOUS COMPENSATION 2.928.308 3/1960 Godbey 84/409 AND/0R FREQUENCY REGULATON Z'ZSS'SZZ 35132? fii"""z;i" 313/35? s l awa e [72] Inventor: Cecil Ih'ank Clifford, Newbridge Works,

Bath, England FOREIGN PATENTS OR APPLICATIONS [22] Filed: July 7, 1970 378,239 7/1964 Switzerland ....58/23 TF [211 App] 52 846 954,944 12/1956 Germany ..58/116 M Primary Examiner-J. V. Truhe [30] Foreign Application Priority Data Assistant Examiner-Reynolds B. A.

July 23, 1969 Great Britain ..37,076/69 and Emmy Gmff Jan. 8, 1970 Great Britain.... ..978/70 March 17, 1970 Great Britain... ....12,723/70 [57] ABSTRACT y 1970 Great Britain 2 13/70 An electromechanical oscillator having an oscillating member which is electrically maintained in mechanical oscillation, in [52] US Cl. ..3l0/22, 58/23 TF, 84/409, which a pair f magnets h opposite poles d fi i a gap i 310/25 carried by a single oscillating member or by one or both tines 2; 2 of a tuning fork, and the rotor is so mounted that the wavy 1 e Bl 5 magnetic tracks pass through the gap or gaps between the pair(s) of magnets. There may be a magnetic member adjacent the free pole of one magnet to provide isochronous compensation or frequency regulation, or a member to pro- [56] References Cited vide isochronous compensation adjacent the free pole of one UNITED STATES PATENTS magnet of a pair and a member to provide frequency regula- 3 581 128 5/1971 tion ad acent the free pole of the other magnet of the pair.

Meisnen ..3 10/21 Nomura et al .t

17 Claims, 22 Drawing Figures w .33; m 3 3 2 2 m N 2 3 SHEET 3 [1F 5 mac mww PATENTEU m 1 8 m2 E M W. In

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mum/3 656/1. EeA/vk cL/FFOIQD 7 V y I PATENTEB JUL] 8 1912 SHEET 5 BF 5 3 Z w a Z w& 0 0 .[K/ M 8 /H 9 F 7 m an. E .0 @7 MW w 5 & u m 2 M m m ELECTROMECI'IANICAL OSCILLATOR WITH ISOCI'IRONOUS COMPENSATION AND/OR FREQUENCY REGULATION This invention relates generally to electromechanical oscillators, and more particularly to an electromechanical oscillator having a rotary output, with means for providing isochronous compensation and/or, if desired, frequency regulation.

Electromechanical oscillators in which the oscillating member is electrically maintained in mechanical oscillation are increasingly being used for timing devices such as clocks, and even wrist watches, and there is a continuing requirement that such oscillators shall be simplified and cheapened and at the same time be made more accurate and reliable. Such oscillators commonly use a simple reed or a tuning fork as the oscillating member.

Electromechanical oscillators having a rotary output are in themselves. known and in some known types the rotary member is in the form of a disk having a wavy magnetic track formed around at least one face thereof. Such a rotary member may be driven by a magnet mounted on the oscillating end of the reed or on one tine of the tuning fork, the magnet being in the form of a ring or frame having a gap across which the two magnet poles face each other, the rotary member being so mounted that the wavy magnetic track passes between the poles of the magnet. The rotary member will hereinafter be referred to as the rotor.

In electromechanical oscillators of the type to which the invention relates a frequency error occurs if the amplitude of oscillation changes. This is partly due to the magnetic interaction between the oscillating member and the rotor and it is desirable to provide isochronous compensation in order that the frequency of oscillation shall remain constant irrespective of the amplitude, or that the amplitude of oscillation shall be kept as constant as possible. Some variation in amplitude is almost impossible to avoid due to variation in the oscillator supply voltage in the type of oscillating under discussion, since the supply to the maintaining amplifier is almost invariable provided by a single tiny dry cell whose voltage from the time it is new to the time when it must be discarded may vary by thirty to forty percent. A second type of error is a frequency error due to the fact that some variation in the natural oscillating frequency is inevitable as between different oscillating members made under normal production conditions so that, in some oscillators at least, the frequency will be incorrect at all amplitudes of oscillation.

The principal object of the invention is to provide an electromechanical oscillator having a rotary output, and which may also contain means to secure isochronous compensation and/or frequency regulation.

The invention consists of an electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member with opposite poles of the magnets defining a gap, and a rotor having a wavy magnetic track around both faces so mounted that the wavy magnetic tracks pass through the gap between the magnets.

In one preferred form the invention consists of an electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of bar magnets carried on the oscillating member with opposite poles of the magnets defining a gap, a rotor having a wavy magnetic track around both faces so mounted that the wavy magnetic tracks pass through the gap between the magnets, and a magnetic element to provide isochronous compensation adjacent the free pole of at least one of the magnets, the magnetic element being so shaped and located as to produce maximum magnetic coupling with the free pole of the magnet at two spaced points in the path of oscillation of the said one magnet.

Preferably the oscillating member is a tuning fork, the supporting member and the magnets being mounted on one tine of the tuning fork, the other tine carrying an equivalent weight to provide balance so that both tines have the same natural frequency of oscillation. Where the oscillating member is a tuning fork there may be a pair of magnets carried on each tine, the rotor being so mounted that the wavy magnetic tracks pass through the gaps between both pairs of magnets, the rotor having wavy magnetic tracks with even numbers of waves. The position of the magnetic element may be adjustable to vary the degree of isochronous compensation provided.

In another preferred form the invention consists of an electromechanical oscillator comprising an oscillating-member which is electrically maintained in mechanical oscillation, a pair of magnets carried on the oscillating member with opposite poles of the magnets defining a gap, a rotor having a wavy magnetic track around both faces so mounted that the wavy magnetic tracks pass through the gap between the magnets, and a magnetic element to provide frequency regulation adjacent the free end of at least one of the magnets, the magnetic element serving to alter the restoring force inherent in the oscillating member throughout the cycle of oscillation of the oscillating member, the magnetic element being movable with respect to the adjacent magnet in order to vary the amount by which the restoring force is altered.

Preferably the magnetic element for providing frequency regulation is movable along a line parallel to the axis of the adjacent magnet, and may be in the form of a screw. The end of the screw nearest the magnet may be frusto-conical.

Selected embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. I is a pictorial diagram showing the essential parts of an electromechanical oscillator according to one form of the invention;

FIG. 2 is a family of curves showing the results obtained in tests carried out on the oscillator of FIG. 1;

FIG. 3 is an elevation of the principal parts of an electromechanical oscillator according to another form of the invention showing magnetic elements arranged to provide respectively isochronous compensation and frequency regulation;

FIG. 4 is a side view of a part of the oscillator of FIG. 3 with the frequency regulating element omitted;

FIG. 5 is an elevation of the flat plate magnetic member used to provide isochronous compensation in the oscillator of FIG. 3;

FIG. 6 shows an oscillating member with an electrical circuit which may be used for electrically maintaining the oscillating member in mechanical oscillation;

FIG. 7 shows a family of curves to show the effect on isochronism of variation in the smallest diameter of the frustoconical ,end of the frequency regulating screw of FIG. 3;

FIG. 8 shows a curve showing the overall frequency regulation which is obtainable with the oscillator of FIG. 3;

FIG. 9 shows a family of curves showing the result obtained in the oscillator of FIG. 3 with and without the frequency regulating screw;

FIG. 10 is an elevation of a further form of electromechanical oscillator according to the invention;

FIG. 11 is a face view of the isochronous compensation member of FIG. 10;

FIG. 12a, 12b and show different stages in the cycle of oscillation in relation to the isochronous compensation member in the oscillator of FIG. 10;

FIGS. 13a, 13b and show an isochronous compensation member having a somewhat different shape to that of FIGS. 11 and 12, and also show three different stages in the cycle of oscillation;

FIG. 14 shows an isochronous compensation member hav ing a still different shape to those of FIGS. 11, 12 and 1-3;

FIG. 15 shows a family of curves to illustrate the results obtained when using the electromechanical oscillator of FIG. 10 without isochronous compensation, with the isochronous compensation member in position and incorrectly adjusted so that it causes over compensation, and with the isochronous compensation member in position and correctly adjusted;

FIG. 16 is a pictorial diagram showing still another form of electromechanical oscillator according to the invention;

FIG. 17 is a diagrammatic side elevation showing an alternative form of isochronous compensation applicable to the oscillator of FIG. 16; and

FIG. 18 is an end view of the arrangement of FIG. 17.

Referring first to FIG. 1, an oscillating member 11 is of the kind which is maintained in oscillation by electrical means in the well-known manner. It may be a single oscillating reed or it may be one tine of a tuning fork, the other tine not being shown, A supporting member 12 is in the form of a small U- shaped bracket, which may be made of a non-magnetic material such as brass, or a non-magnetic and non-metallic material such as a synthetic plastics material, and is mounted on the end of the member 11. The two arms of the bracket respectively carry two magnets 13 and 14, the ends of the magnets inside the arms of the bracket being formed to present rectangular pole ends 15 and 16 of opposite polarity to the magnetic track formed around a driving wheel 17. The rectangular pole ends are not essential and circular pole ends may be used if desired. A rotor is mounted on a spindle 18 which may be arranged to drive the mechanism of a timing device such as a clock. A rotor of the type shown at 17 is in itself known and was originally used many years ago as a magnetic escape wheel in a magnetic escapement in which the spindle 18 was driven by means such as a spring or an electric motor and the wheel was allowed to escape" at a rate determined by the frequency of oscillation of the oscillating member by which it was controlled. In the present case the rotor is used to drive the spindle 18 without the need for an additional power source such as an electric motor or a spring.

A magnetic element 19 for providing isochronous compensation consists of a small plate made of a magnetic material of high permeability and low retentivity, such as that known by the Registered Trade Mark MUMETAL, and is advantageously so mounted that its position in relation to the free pole 20 of the magnet 14 is adjustable. The adjustment may be in the direction of the length of the element 19 or it may be towards and away from the pole 20. The element 19 is formed with a slot 21. 1

In operation, the natural frequency of the oscilling assembly is governed by the combined weight of the oscillating member 11, the bracket 12 with magnets 13 and 14, and the stiffness of the oscillating member, which governs its natural restoring force. It is, however, also influenced by the magnetic interaction between the pole 20 of the magnet 14 and the plate 19. As the member 11 oscillates the rotor 17 is rotated inv one direction or. the other due to the magnetic interaction between the magnetic poles l5 and 16 and the wavy magnetic track on the rotor which is defined by slots 22 and openings 23 punched in the disk constituting the rotor 17 so as to define the wavy magnetic track whose median path is defined by the dotted line 24. When the oscillating assembly constituted by parts 11 to 14 moves past and away from the central rest position a progressively increasing restoring force is developed by the oscillating member 11, tending to restore the assembly to the central rest position. However, the attraction between the magnet pole 20 and the nearest leg of the plate 19 pulls the oscillating assembly away from the central rest position towards a position which provides maximum overlap between the pole 20 and the said nearest leg of the plate 19. During this part of the movement the magnetic pull acts against the restoring force. When the position of maximum overlap between the pole 20 and the leg of the plate 19 is reached the magnetic pull is entirely along the axis of the magnet, and this has no effect on the sideways pull, which falls to zero. Hence the magnetic force opposing the restoring force falls to zero. If and when the oscillating assembly moves past the position of maximum overlap a sideways pull develops in the opposite direction and the magnetic pull is added to the restoring force. Hence the isochronous compensation member 19 acts to decrease the oscillation frequency up to the position of maximum overlap and to increase the frequency if it passes the position of maximum overlap. That is to say, it tends to keep the oscillation frequency constant. The plate 19 therefore functions as a true isochronous compensation member. The amount of compen sation may be varied by moving the plate 19 closer to, or away from, the magnet pole 20 or by moving the plate lengthwise, that is, upwards or downwards in FIG. 1.

Where the oscillating member is a tuning fork a bracket corresponding with bracket 12 and magnets corresponding with the magnets 13 and 14 may be mounted upon the second tine and these may be arranged to engage and co-operate with the wavy magnetic track at diametrically opposite points on the rotor 17, the wavy magnetic tracks having an even number of waves. Such an arrangement is illustrated diagrammatically in FIG. 16, where a second tine 11' carrying a bracket l2'and a pair of magnets 13, 14 is shown in broken outline. Alternatively a balancing weight indicated diagrammatically by 12' in the embodiment of FIG. 4, may be mounted on the second tine to ensure that its natural frequency of oscillation is substantially the same as that of the tine 11.

A second isochronous compensation element 19, shown in broken outline in FIG. 1, may be placed adjacent the pole 25 at the free end of the magnet 13, to increase the amount of compensation.

FIG. 2 shows, in the form of curves, the results of tests made with an electromechanical oscillator of the kind shown in FIG. 1. The curves are all drawn to a base of voltage of the amplifier power supply and this voltage ranges from 0.8 to 1.6 volts. The upper group of curves has a vertical scale ranging from -70 to 40 and is marked seconds per day", this being the time lost by the oscillating member (a tuning fork) as compared with its true natural frequency. The lower group of curves is drawn to a vertical scale ranging from 30 to l0 seconds per day.

Referring first to the upper group of curves, two tests were made to find the effect when the pole of the magnet 25 was rather close to one of the brass side plates (not shown) which support the oscillator and the gear train of a timing mechanism (not shown) which is coupled to the spindle 18. In these two tests no rotor was used and no isochronous compensation was provided. In the first test, shown by curve 26, the magnet pole was 0.05 inch from the brass plate and in the second test, curve 27, the magnet pole was almost touching the brass plate, so that small eddy currents were probably induced in the brass. plate, producing a reduction in fork frequency which is constant over the voltage range. In these tests the fork was not loaded by the rotor and the fact that the 1 time loss increased as the. voltage increased is due to increasing amplitude of fork tine oscillation.

For the dotted line curve 28 the rotor 17 (FIG. 1) was introduced, but without isochronous compensation. In this case the voltage was not reduced below 1.0 volt because the oscillator did not operate satisfactorily at this low voltage when loaded by the rotor. It will be seen that the tine loss was now a maximum at the low voltage, and diminished as the voltage was increased. However, there is a considerable variation in the time loss over the voltage range. If the time loss is constant over the voltage range it can be allowed for, and in such a case the curve would be a horizontal straight line.

For the next test, represented by the chain dotted curve 29, the compensating magnetic element 19 (FIG. 1) was introduced, its form being that shown in FIG. 5. It had a width of 0.04 inch, a slot 0.013 inch wide, a thickness of 0.014 inch, and was spaced 0.008 inch from the magnet pole 20. This was animprovement in that the curve was more nearly horizontal. For the next test, shown in full line curve 30, the compensating element 19 was of the form shown in FIG. 5 but its thickness was 0.02 inch. This produced an increased time loss and the slope was still greater than was desirable. It appeared that the oscillator was over-compensated.

To check this last point the 0.014 inch thick element had its thickness reduced by one-half i.e. to 0.007 inch. For this test the parts were arranged as shown in FIG. 1, with the element 19 covering the full area of the magnet pole 20. This produced the results shown in curve 31. A new element was next made from material 0.014 inch thick, with a narrower slot, that is 0.010 inch wide, and the element was spaced by 0.007 inch from the magnet pole 20. This produced the result shown in curve 32. The element 19 was then raised in relation to the magnet pole 20 so that the element only covered one-half the area of the magnet pole, as illustrated in the'thumbnail sketch adjacent curve 33. This produced the result shown in curve 33.

A consideration of curve 32 indicates that the performance of the compensated oscillator is extremely good. It falls off somewhat when the voltage drops below 1.1 volts but between 1 l and 1.6 volts the time loss is substantially constant at about seconds per day, the variation in time loss with a voltage variation between 1.1 and 1.6 volts being in the order of only 2 seconds per day.

If desired a compensatingelement, similar to the element 19, may be placed adjacent the magnet 13 as well as the magnet 14. The two elements could, if desired, be of different shape or form.

lsochronous compensation provides correction for variations in frequency which would otherwise take place over a period of months whilethe oscillator is in operation. In manufacturing quantities of small tuning forks it is inevitable that there are small differences between the natural frequencies of different forks. When a tuning fork is operating, transducers (described later in connection with FIG. 6) must be employed to provide the drive in conjunction with a maintaining circuit, often a single transistor amplifier. The transducers load the fork to some extent. Where a rotary output is required the rotor must be driven by the tuning fork, and this provides a further lead All these factors affect the operating frequency of the tuning fork. The frequency error is a constant error. Where, as is usual, the clock or timing device is driven from the rotor of the electromechanical oscillator through a gear train it is essential that the tuning fork should operate at its predetermined frequency and the invention provides frequency regulating means by which the initial frequency error may be corrected. One means for providing frequency regulating according to the invention is shown in FIGS. 3 to 9, which will now be described.

FIG. 3 is an elevation of the electromechanical oscillator shown in FIG. 1 and shows the mechanical oscillating member 11, the supporting member 12, magnets 13 and 14, with poles 15 and 16. The rotor 17 is carried on the spindle 18 (not seen) the direction of oscillation of the member 11 in FIG. 3 being perpendicular to the plane of the paper and in the direction of the double-headed arrow 34 in FIG. 4. The direction of the wavy magnetic track is indicated by the dotted line 24 in FIG. 4.

The magnetic element 19 for providing isochronous compensation may be the same as that used in the embodiment of FIG. 1 and shown in FIG. 5. The isochronous compensation may be the same as that used in the embodiment of FIG. 1 and shown in FIG. 5. The isochronous compensation member 19 is formed with the slot 21 as previously described.

Carried in an internally screw-threaded support 35 is a frequency regulating element in the form of a screw, generally indicated at 36, having a large diameter knurled or milled end portion 37. The regulating screw 38 is made of a'magnetic material such as mild steel or soft iron and has a frusto-conical end 38. Means (not shown) may be provided to lock the regulating screw 36 in position after adjustment with respect to the free pole or end 25 of the magnet 13, and the locking means may be in theform of a friction lock or a positive lock provided by a locknut.

As the regulating screw 36 is screwed towards and away from the magnet 13 the magnetic attraction between the screw and the magnet 13 is varied, since the length of the flux path is altered, and as the screw is brought closer to the magnet the pull on the magnet increases, so that the natural restoring force provided by the tine is changed and the natural frequency of the fork tine is increased.

In discussing the action of the isochronous compensation element 19 in connection with FIG. 1 it was shown that the effect is alternately to add to, and subtract from the restoring force of the oscillating member during each cycle of oscillation. Hence, although the element 19 has a powerful effect in compensating errors in isochronism which may result from changes in operating conditions, e.g., changes in battery voltage, its effect on the average restoring force of the oscillating member is very small and its effect on the operating frequency is correspondingly small. On the other hand the effect, of a properly designed frequency regulating element is to add to the restoring force of the oscillating member throughout the stroke and proportional to deflection and this directly alters the frequency with no appreciable effect on isochronism. With the two members arranged as shown, with correctly chosen parameters, the effect of the member 19 is to provide isochronous compensation and that of the element 36 is to provide frequency regulation. A second frequency regulating element, shown in broken outline at 36' in FIG. 3, may be provided adjacent the free pole 20 of the other magnet 14 of the pair of magnets 13, 14.

FIG. 6 shows a conventional circuit and one form of transducer by which an oscillating member is maintained in mechanical oscillation by electrical means. The oscillating member shown in FIG. 6 is a single reed 3? carried on a support 40. Although most of the Figures show tuning forks the invention may equally well be applied to electromechanical oscillators containing single reeds. A single coil 41 comprises a ferro-magnetic core 42 and a winding, one end of which is connected by a lead 43 to the input of an amplifier 44. A driving coil 45 is provided with a ferro-magnetic core 46 and has one end of its winding connected by a lead 47 to the output of the amplifier 44. The two remaining ends of the windings of the signal and driving coils are connected by a lead 48 to a common ground or earth point 49. A magnet 50 co-operates with the wavy magnetic track of a rotor (not shown) similar to the rotor 17 in order to drive the rotor.

As already stated, one of the difficulties experienced with electromechanical oscillators of the kind under discussion is that the oscillation amplitude changes with changes in battery voltage. The main function of the isochronous compensation member is to reduce the variation in frequency due to voltage changes, while the main function of the frequency regulating member is to enable the frequency, which controls the speed of the clock or timing device, to be regulated. The six curves of FIG. 7, respectively 51, 52, 53, 54, 55 and 56, show the effect on isochronism of frequency adjusting screws with the diameters of their frusto-conical ends ranging from 0.2 millimetre, in 0.2 millimetre steps, up to 1.2 millimetres. Along the base of the curves voltage levels ranging from 1.0 volts to 1.6 volts are shown and a vertical scale indicates an increment of 10 seconds per day. It will be noted that the general form of curves 51 and 54 is a little different to those of the others and this is due to particular combinations of effects relating to those particular sizes.

When the regulator was screwed back so that the gap between the end of the adjusting screw and the adjacent end of the magnet was 2 millimetres all the curves lay between the dotted lines 61 and 62. If curve 55, relating to a frequency regulating screw having an end diameter of 0.8 millimetre, is compared with the curves 61 and 62 it will be noted that curve 55 has substantially the same shape as curves 61 and 62 between 1.6 and 1.2 volts, but by screwing the regulating screw in towards the adjacent magnet the frequency has been increased to a considerable extent. This is the best example among the different arrangements tested to show that by correctly selecting the parameters of the associated parts it is possible to provide an arrangement in which the frequency may be regulated with virtually no effect at all on the isochronism.

It will be understood that if the sizes or other characteristics of the operating parts were altered it would be necessary to change the sizes or shapes of the isochronous compensation and/or frequency regulating elements in order to secure equally effective results. It will also be understood from the generally known characteristics of magnetic circuits and materials that the frequency regulating member, instead of being moved in a direction parallel to the axis of the adjacent magnet, could be moved across the axis of the adjacent magnet, or in another direction, provided that its shape and size were correctly chosen.

FIG. 8 shows a curve 57 drawn to a base of screw end diameter and illustrates the maximum amount of time or frequency regulation which can be obtained and a study of the curve 57 will show that with the minimum screw end diameter of 0.2 millimetres the range of regulation obtainable is about 80 seconds per day while with the largest screw diameter of 1.2 millimetres the possible range of regulation is about 235 seconds per day, or nearly four minutes, but usually only about 40 seconds per day is used.

FIG. 9 shows a further family of three curves drawn to a base of voltage, ranging from 1.0 volts to 1.6 volts, and with a vertical scale in which an interval of 10 seconds per day is shown. The full line curve 58 shows the time (or frequency) error voltage dependence with no adjusting screw. The chain dotted curve 59 shows the error voltage dependence with an adjuster capable of a range of regulation of 12 seconds per day, with the gap between the regulator screw and the magnet set to 2 millimetres, while the dotted line curve 60 shows the time or frequency error voltage dependence with an adjusting screw having a range of 225 seconds per day and the gap between the end of the regulating screw and the adjacent end of the magnet set at 0.1 millimeter. Even with this small gap and large range of regulation isochronism is hardly affected.

Curve 60 has been placed close to curve 58, instead of 225 seconds per day higher on the sheet, to facilitate comparison of the shapes of the curves.

In the embodiment of FIG. 1 the force due to the magnet 14 acting upon the isochronous compensation element 19 varies between particular minimia and maxima during each oscillation cycle of the oscillating member/The rate at which the magnetic attraction changes, and the minimum and maximum level thereof, which might be referred to as the isochronous compensation characteristic, may be altered by altering the shape of the isochronous compensation element. isochronous compensation elements of different shapes are shown in FIGS. 10 to and these will now be described as applied to the electromechanical oscillator of FIGS. 1 and 3.

Referring to FIGS. 10 to 15, an elevation of the electromechanical oscillator illustrated in FIGS. 1 and 3 is shown, with its oscillating member 11, the- U-shaped supporting member 12, the magnets 13 and 14 formed with pole ends 15 and 16, and rotor 17. It differs from the oscillator of FIGS. 1 and 3 in that a different type of isochronous compensation element 63 is shown in place of the element 19.

The isochronous compensation element 63 is disposed adjacent the free pole (that is the pole which is not associated with the rotor 17) of the magnet 14. The frequency regulator of FIG. 3, indicated in dotted lines at 36, may be included if desired, or alternatively a second isochronous compensation member 63 may be used instead.

FIG. 11 shows the shape of the isochronous compensation member 63 when looking at it in the direction of the arrow 64 of FIG. 10. It is of generally elongate shape having corners 65 and 66 which are conveniently right-angled and having partcircular portions cut out at 67 and 68. The direction of oscillation of the oscillating assembly is indicated by the arrow 69. The general shape of the compensating member provides two regions, respectively 70 and 71, each of which presents a comparatively large area, and it is arranged that the centres of these regions are separated by a distance substantially equal a particular or mean amplitude (e.g. the amplitude at 1.3 volts) of oscillation of the magnet 14, so that a maximum magnetic coupling with the free pole of the magnet occurs at these two positions. This is illustrated in more detail in FIGS. 12a, 12b and 120.

Referring first to FIG. 12b, the centres of the regions of maximum magnetic coupling are indicated respectively at 72 and 73 and with the magnet 14 oscillating at the mean amplitude its two positions are indicated respectively at 74 and 75. In the one position 74 the axis of the magnet 14 coincides substantially with the point 72 and at the other position 75 the axis of the magnet coincides substantially with the point 73 and hence the magnetic coupling is at is maximum.

In FIG. 12a a condition is shown in which the magnet is oscillating at a higher amplitude than the mean amplitude, so that it moves in one direction to a position 76 and in the other direction to a position 77. It will be evident that once the axis of the magnet moves outwardly past the point 72 or the point 73 (FIG. 12b) the isochronous compensation element 63 will exert a restraining force on the magnet, so that effectively the restoring force is increased as soon as the amplitude exceeds the mean level. FIG. 12c shows the magnet 14 in its central position i.e. with zero amplitude of oscillation, and it will be evident that as soon as it moves slightly from the central position the magnetic interaction between the pole of the magnet and the member 63 will tend to pull the magnet outwardly towards one or other of the positions shown in FIG. 12b, in which the axis of the magnet coincides with the point 72 or the point 73.

FIG. 12b shows the amplitude of oscillation which was achieved in an oscillator having an isochronous member of the FIG. 11 type with an energizing E.M.F. of 1.2 volts, while FIG. 12a shows the difference resulting from an increase of E.M.F. to 1.5 volts.

FIGS. 13a, 13b and 13c correspond respectively with FIGS. 12a, 12b and 120 but show the movements of the magnet 14 with a differently shaped isochronous compensation member which is indicated by reference 78. In this case the member has the outer right-angled corners and 66 as in the case of the member 63 but in place of the part-circular portions 67 and 68 the shape is defined by two straight portions, respectively and 80, which are set at 30 to the longitudinal centre line of the member 78.

FIG. 14 shows the shape of a further isochronous compensation member indicated by reference 81, in which the straight portions 79 and 80 of FIG. 13 are retained but the straight sides and corners 65 and 66 of the members of FIGS. 12 and 13 are replaced by particular boundaries, respectively 82 and 83.

The exact shape of the compensation member may be varied according to the particular type of electromechanical oscillator with which is is to be used and the shape plays an important part in the effectiveness with which the member controls theoscillation frequency.

FIG. 15 contains a family of curves to illustrate the effect of an isochronous compensation member of the kind illustrated in FIGS. 11 and 12 when used in an electromechanical oscillator of the kind illustrated in FIG. 10. The three curves are drawn to a horizontal scale of voltage, that is, the voltage applied to the amplifier which maintains the oscillation of the oscillating member, and the voltage range is between 1.0 and 1.6 volts. A rate of 10 seconds per day is indicated on the vertical scale.

The curve 84 was taken without isochronous compensation and it shows a time error up to 18 0 seconds per day for a voltage change from 1.5 volts to 1.0 volts. The curve 85 was taken with the isochronous compensation member deliberately placed much too close to the magnet (spaced from it by only 0.003 inch 0.08 millimeter) so that the oscillator was heavily over-compensated. This produced a voltage dependence of the error in the opposite direction, with an even steeper curve, the error change being of the order of seconds per day for a voltage change of only 0.3 volts. The curve 86 was taken In the embodiment of FIG. 1 the pole face of the magnet 14 overlaps the two sides of the slot 21 in the central rest position. When the magnet, during its oscillation cycle, moves past the central rest position it is attracted to one leg of the isochronous compensation element 19, and when the axis of the magnet is opposite the centre of this leg the sideways pull falls to zero, and it builds up in the opposite direction when the magnet moves beyond this leg. The maximum pull depends upon the shapes of the co-acting magnetic parts. For a given size and power of magnet the maximum sideways pull,

and the rate of change of this pull with movement of the magnet during the oscillation cycle, depend upon the relative shapes of the co-acting magnetic parts. In the embodiments of FIGS. to 14 there is a much smaller sideways pull initially since the area of overlap between the magnet pole face and the isochronous compensation element 63, 78 or 81 changes comparatively slowly as the magnet moves and it is the rate of change of magnetic coupling which determines the sideways pull. On the other hand, when the magnet moves beyond the position of maximum overlap, illustrated in FIG. 12b, for example, the rate of change is more rapid so the retarding pull on the magnet increases more rapidly. Hence the embodiments of FIG. 1, on the one hand, and FIGS. 10 to 14 on the other hand, provide substantially different isochronous compensation characteristics. There are also differences, albeit of a smaller order, between the characteristics of the elements shown in FIGS. 11, 13 and 14. The invention makes it possible to provide a much sharper isochronous compensation characteristic, with a much higher maximum pull and a more rapid rate of change, than either of the types so far discussed.

, Embodiments having such sharper characteristics are shown in FIGS. 16 to 18 which will now be described.

Referring first to FIG. 16, the oscillating assembly is similar to that shown in FIG. 1, having the oscillating member 11, the supporting member 12, the two magnets 13 and.14, with their rectangular pole ends and 16, and the rotor 17 mounted on the spindle 18.

A magnetic element 19 for providing isochronous compensation is placed adjacent the free end 20 of the magnet 14. The magnet 14 is conveniently made of a magnet steel such for example, as that sold under the Trade Name Vicalloy, which is a high cobalt magnet steel containing a proportion ofvanadium. It is also a type of steel which may be forged. or swaged and this property is made use of to upset" the end 87 of the magnet 14 so that the end pole face 88, indicated partly in full lines and partly in dotted lines, presents an area which is long and narrow, and substantially rectangular. In one practical embodiment the magnet 14 may have a diameter of l millimeter. The rectangular pole face 16 is formed by cutting away parts of the ends at an oblique angle to form this pole face while the end 87 may be produced by forging down to a width of 0.4 millimeter so that the end is spread to provide a pole face 88 having a height of about 2 millimeters. The pole face 88 is perpendicular to the axis of the magnet 14.

The isochronous compensation element 93 is conveniently made from a strip of high permeability nickel iron alloy, which may be of the kind known by the Registered Trade Mark MU- METAL, and for an oscillator having a magnet 14 of the dimensions suggested above the strip may conveniently have a width of 2 millimeters and a thickness of 0.4 millimeter. The strip is bent to a U-shape to form arms, respectively 89 and 90, and the end faces, respectively 91 and 92, are finished square to the length of the arms so that the two end faces 91 and 92 are parallel with the pole face 87 of the magnet. The element 93 is placed symmetrically with respect to the axis of the magnet 14 so that in the position of rest the pole face 87 faces the center of the gap 94 between the arms 89 and 90. The gap 94 is determined according to the desired amplitude of oscillation of the oscillating parts, which include the tine 11, and which oscillate in the direction indicated by the double-headed arrow 95. In an oscillator having the dimensions suggested above the gap 94 could be 0.4 to 0.8 millimeter. The gap between the pole face 88 and the plane including the end faces 91 and 92 measured along the axis of the magnet 14, may be of the order of 0.25 millimeter but the element 93 is made movable along the axis of the magnet 14, whereby this gap may be adjusted in order to vary the amount of isochronous compensation which is provided, so that the optimum conditions may be selected. 1

In operation, once oscillation has started, as the pole face 88, moving in one direction or the other, passes the center point it will be attracted by the arm 89 or 90 towards which it is moving and this attraction will oppose the natural restoring force inherent in the tine 11. The instantaneous restoring force exerted by the tine 11 increases as the pole face 88 moves progressively further from the center point, and the attraction provided by the pole face 88 increases as it approaches the pole face 91 or 92. However, once the pole face 88 begins to overlap the face 91 or 92 the sideways magnetic attraction begins to decrease rapidly, whereas the restoring force provided by the tine 11 continues to increase. When a point is reached at which the pole 88 is just opposite the face 91 or 92 the sideways magnetic attraction has fallen to zero and instead there is an end pull on the magnet 14 which has no effect on the operation of the oscillator. Continued movement of the oscillating assembly in the same direction now produces a reversed effect. A sideways magnetic pull is exerted tending to pull the pole face 88 back to the position in which it is opposite the face 91 or 92 while the restoring force exerted by the tine 11 continues to increase. Hence the sideways pull of the magnet is now added to the restoring force. These conditions apply when the oscillating parts are moving in either direction. Because of the long narrow pole faces and the gap between the pole faces 91 and 92 this arrangement provides a very high maximum pull and high rates of change of pull. The amount of compensation which is provided may readily be adjusted by moving the element 93 axially of the magnet 14 since over-compensation can be as undesirable as under-compensation. 1 In the embodiment of FIG. 16 the arms 89 and 90 lie parallel to the axis of the magnet 14. However, the same effect can be produced by turning the element 93 at right angles and placing it below or above the end 87 of the magnet 14, the end 87 being extended. This is illustrated in FIGS. 17 and 18, which only show the modified form of magnet, referred to as 14a and the isochronous compensation member 96, which may also be made from MUMETAL bent into a U Shape, as illustrated. The flat portion formed on the end of the magnet 14a is longer, as indicated at 97, and the gap 98 between the two arms 99 and 100 of the magnet 96 may be the same as the gap 94. Adjustment is carried out by moving the member 96 up and down in order to vary the gap 101 between this member and the end 97 of the magnet.

The free pole of the magnet 13 may be used to provide frequency regulation, for example by the means described in relation to FIG. 3.

The characteristics of different types of electromechanical oscillators may vary very widely, due to differences in the restoring force of the oscillating member, different types and weights of magnets, different weights of arious types of transducer, and other factors. From the foregoing description it will be evident that by the use of the invention it is possible to provide isochronous compensation means having characteristics which are very closely matched to those of any type of oscillator. The invention also makes it possible to provide means for frequency regulation which are equally closely matched to the characteristics of any type of oscillator. Moreover, both isochronous compensation and frequency regulation may be provided if desired.

Various modifications may be made in the embodiments of the invention which are illustrated. For example the reed or tuning fork could be of the compound reed type as disclosed in our British patent application No. l,l84,669.

I claim:

1. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet.

2. An oscillator as claimed in claim 1 comprising two magnetic elements to provide isochronous compensation, the magnetic elements being mounted adjacent the free poles of both magnets.

3. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet, and said magnetic element comprising a flat plate of elongate form which is slotted to form two legs, the plate being so mounted that it lies in a plane parallel to the path of oscillation of the oscillating member and the longer dimension of the plate is substantially perpendicular to the said-path of oscillation.

4. An oscillator as claimed in claim 3 comprising a supporting member mounted on the oscillating member, the two magnets being carried on the supporting member.

5. An oscillator as claimed in claim 3 in which the oscillating member is a tuning fork, the magnets being mounted on one tine of the tuning fork, the other tine carrying an equivalent weight to provide balance so that both tines have substantially the same natural frequency of oscillation.

6. An oscillator as claimed in claim 3 in which the oscillating member is'a tuning fork, comprising a said pair of magnets on each tine of the tuning fork, the rotor being so mounted that the wavy magnetic tracks pass through the gaps between both pairs of magnets, the rotor having wavy magnetic tracks with even numbers of waves.

7. An oscillator as claimed in claim 3 in which the position of the plate is adjustable towards or away from the adjacent magnet and/or in the longitudinal direction of the plate.

8. An electromechanical oscillator comprising an oscillating member which is-electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet, and said magnetic element comprising a plate of elongate form lying in a plane parallel to the path of oscillation with the longer dimension of the plate substantially parallel to the path of oscillation, the plate having a narrow or waisted central portion with two wider portions spaced on either side thereof to form the two points at which maximum magnetic coupling is produced.

9. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet, and wherein said free pole is formed to provide a long narrow substantially rectangular pole face lying in a plane parallel to the path of oscillation and perpendicular to the axis of the magnet, the pole face having its longer dimension substantially perpendicular to the path of oscillation, and the magnetic element to provide isochronous compensation is formed to present two similar rectangular faces spaced on either side of the central rest position of the magnet.

10. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet and wherein said free pole of the magnet is formed to provide a long narrow substantially rectangular pole face lying in a plane parallel to the axis of the magnet and substantially parallel to the path of oscillation, the pole face having its longer dimension parallel to the axis of the magnet, and the magnetic element to provide isochronous compensation is formed to present two similar rectangular faces spaced on either side of the central rest position of the pole face.

11. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide frequency regulation adjacent the free pole of at least one of the magnets, the magnetic element affecting the resultant restoring force acting on the oscillating member throughout each cycle of oscillation of the latter.

12. An oscillator as claimed in claim 11 in which the magnetic element is movable with respect to the adjacent magnet in order to vary the amount by which the restoring force is altered.

13. An oscillator as claimed in claim 12 in which the magnetic element for providing frequency regulation is movable along a line parallel to the axis of the adjacent magnet.

14. An oscillator as claimed in claim 11 in which the magnetic element for providing frequency regulation is in the form of a screw.

15. An oscillator as claimed in claim 14 in which the end of the screw nearest the magnet is frusto-conical.

16. An oscillator as claimed in claim 11 comprising a second magnetic element to provide frequency regulation adjacent the free pole of the second magnet of the pair.

17. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member, said magnets having a pair of opposite poles defining a gap and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap said rotor being driven upon oscillation of said oscillating member, a first magnetic element to provide isochronous compensation located adjacent the free pole of one magnet, said first magnetic element having maximum magnetic coupling with the free pole of the said one magnet at two spaced points in the path of oscillation of the said one magnet, and a second magnetic element to provide frequency regulation adjacent the free pole of the other magnet, said second magnetic element affecting the restoring force acting on the latter. 

1. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet.
 2. An oscillator as claimed in claim 1 comprising two magnetic elements to provide isochronous compensation, the magnetic elements being mounted adjacent the free poles of both magnets.
 3. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet, and said magnetic element comprising a flat plate of elongate form which is slotted to form two legs, the plate being so mounted that it lies in a plane parallel to the path of oscillation of the oscillating member and the longer dimension of the plate is substantially perpendicular to the said path of oscillation.
 4. An oscillator as claimed in claim 3 comprising a supporting member mounted on the oscillating member, the two magnets being carried on the supporting member.
 5. An oscillator as claimed in claim 3 in which the oscillating member is a tuning fork, the magnets being mounted on one tine of the tuning fork, the other tine carrying an equivalent weight to provide balance so that both tines have substantially the same natural frequency of oscillation.
 6. An oscillator as claimed in claim 3 in which the oscillating member is a tuning fork, comprising a said pair of magnets on each tine of the tuning fork, the rotor being so mounted that the wavy magnetic tracks pass through the gaps between both pairs of magnets, the rotor having wavy magnetic tracks with even numbers of waves.
 7. An oscillator as claimed in claim 3 in which the position of the plate is adjustable towards or away from the adjacent magnet and/or in the longitudinal direction of the plate.
 8. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet, and said magnetic element comprising a plate of elongate form lying in a plane parallel to the path of oscillation with the longer dimension of the plate substantially parallel to the path of oscillation, the plate having a narrow or waisted central portion with two wider portions spaced on either side thereof to form the two points at which maximum magnetic coupling is produced.
 9. An electromechanical oscillator comprising an oscillating meMber which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet, and wherein said free pole is formed to provide a long narrow substantially rectangular pole face lying in a plane parallel to the path of oscillation and perpendicular to the axis of the magnet, the pole face having its longer dimension substantially perpendicular to the path of oscillation, and the magnetic element to provide isochronous compensation is formed to present two similar rectangular faces spaced on either side of the central rest position of the magnet.
 10. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide isochronous compensation located adjacent the free pole of at least one said magnet, said magnetic element having maximum magnetic coupling with said free pole at two spaced points in the path of oscillation of the magnet and wherein said free pole of the magnet is formed to provide a long narrow substantially rectangular pole face lying in a plane parallel to the axis of the magnet and substantially parallel to the path of oscillation, the pole face having its longer dimension parallel to the axis of the magnet, and the magnetic element to provide isochronous compensation is formed to present two similar rectangular faces spaced on either side of the central rest position of the pole face.
 11. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member said magnets having a pair of opposite poles defining a gap, and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track which passes through said gap, said rotor being driven upon oscillation of said member, and a magnetic element to provide frequency regulation adjacent the free pole of at least one of the magnets, the magnetic element affecting the resultant restoring force acting on the oscillating member throughout each cycle of oscillation of the latter.
 12. An oscillator as claimed in claim 11 in which the magnetic element is movable with respect to the adjacent magnet in order to vary the amount by which the restoring force is altered.
 13. An oscillator as claimed in claim 12 in which the magnetic element for providing frequency regulation is movable along a line parallel to the axis of the adjacent magnet.
 14. An oscillator as claimed in claim 11 in which the magnetic element for providing frequency regulation is in the form of a screw.
 15. An oscillator as claimed in claim 14 in which the end of the screw nearest the magnet is frusto-conical.
 16. An oscillator as claimed in claim 11 comprising a second magnetic element to provide frequency regulation adjacent the free pole of the second magnet of the pair.
 17. An electromechanical oscillator comprising an oscillating member which is electrically maintained in mechanical oscillation, a pair of magnets carried by the oscillating member, said magnets having a pair of opposite poles defining a gap and a pair of free poles spaced remotely from said gap, a rotor having a wavy magnetic track whIch passes through said gap said rotor being driven upon oscillation of said oscillating member, a first magnetic element to provide isochronous compensation located adjacent the free pole of one magnet, said first magnetic element having maximum magnetic coupling with the free pole of the said one magnet at two spaced points in the path of oscillation of the said one magnet, and a second magnetic element to provide frequency regulation adjacent the free pole of the other magnet, said second magnetic element affecting the restoring force acting on the oscillating member throughout the cycle of oscillation of the latter. 